Add or Subtract Days from a Date

How it works

Choose a start date, decide whether to add or subtract, and enter an amount in years, months, weeks and days. You can combine them, for example 1 year, 2 months and 10 days. The result is the new date shown with its weekday, its position in the year (day 1 to 365 or 366), and the number of calendar days between the start and the result.

Calendar mode works in two steps. First, years and months are combined into a single number of months (years x 12 + months) and applied to the start date in one move. If the target month is shorter than the start day, the date is clamped to the last day of that month. January 31 plus one month is February 28, or February 29 in a leap year. February 29 plus one year is February 28. March 31 minus one month is February 28 or 29. Second, weeks x 7 + days are added or subtracted as plain calendar days, which never need clamping.

That order is fixed, and it matters. Start from January 30, 2027 and add 1 month and 1 day: the month step gives February 28, then one day gives March 1. If you added the day first (January 31) and the month second, you would land on February 28. Likewise, adding 2 months to January 31 gives March 31, while adding 1 month twice in a row gives February 28 and then March 28. Enter the whole span at once, as it is written in your contract or plan.

Weekdays-only mode counts Monday to Friday. The amount is weeks x 5 + days, the start day itself is not counted, and Saturdays and Sundays are skipped. Years and months are not available here. If you start on a weekend, the weekend days are skipped like any others: Saturday plus 1 weekday is Monday, and Saturday or Sunday minus 1 weekday is Friday. An amount of zero returns the start date unchanged, even on a weekend. Public holidays are not excluded, see the notes below.

Years 1 to 9999 are accepted. Dates follow the proleptic Gregorian calendar, meaning today's leap-year rules are applied backwards indefinitely. For dates before the Gregorian reform (which different countries adopted between 1582 and the 20th century), the result will not match the Julian dates used at the time. Everything runs in your browser, and no date you enter is sent to a server.

Examples

90 days from a date. Start on Friday, October 9, 2026 and add 90 days. October has 22 days left, November 30 and December 31 bring the total to 83, and 7 more days reach January 7, 2027, a Thursday. Check: 90 days is 12 weeks and 6 days, and Friday plus 6 days is Thursday.

6 months from August 31. Adding 6 months to August 31, 2026 targets February 31, 2027, which does not exist, so the result is Sunday, February 28, 2027, 181 calendar days after the start. In 2028 the same calculation would end on February 29.

A 30-weekday deadline. Start on Wednesday, October 14, 2026 and add 30 weekdays (6 weeks). Each full week of 5 weekdays returns to the same weekday, so the result is Wednesday, November 25, 2026, 42 calendar days later. For comparison, adding 30 calendar days to the same start gives Friday, November 13.

Subtracting a year from a leap day. February 29, 2028 minus 1 year has no matching date in 2027, so the result is Sunday, February 28, 2027. The two dates are 366 days apart, because the span contains a leap day. Adding one year back from February 28, 2027 gives February 28, 2028, not February 29, so month-end clamping is not reversible.

An invoice due date. An invoice dated October 9, 2026 with a 30-day term falls due on Sunday, November 8, 2026. Whether payment on a Sunday counts, or rolls to Monday, depends on your agreement, not on this calculation.

Things to watch for

• Weekdays are not working days. Only weekends are skipped. A public holiday that falls on a Monday to Friday is still counted. Which days are holidays, and whether bridge days are taken, varies by country and year, so add those days yourself.
• The start day is not counted. Adding 1 day to Monday gives Tuesday. If your agreement says "within 10 days including the first day", enter 9.
• Legal and contractual periods have their own counting rules. Notice periods, return windows, lease terms and limitation periods may count the first day, skip holidays or end on the next business day. Those rules differ by country and by document, and the contract or the law governs. Use this tool to get the calendar arithmetic right, not to settle the rule.
• Months are not 30 days. If a deadline says "3 months", use the months field. If it says "90 days", use the days field. The two land one or two days apart, depending on which months are involved.
• Clamping can hide the original day. After February 28, the original 31st is lost, so do not chain several one-month steps when one longer step gives the correct answer.
• Time of day and time zones are ignored. The tool works with calendar dates only.

To measure the gap between two dates you already have, use the date difference calculator. To work out how old someone is, or how long since a start date in years, months and days, use the age calculator.